Worcester Bosch Anti Fast Cycling

[John Carroll]

Some one asked me some time ago  to have a look at this and explain how it works, I got a lot of info from  another site and I think this is how it works.

It uses time and temperature vs time only in most fairly simple anti fast cycling methods, Vaillant use a table of time+target temp.

 

WB 2.3B   Anti Fast Cycle Time, (settable) 3 to 45 minutes, default 5 minutes.

      2.3.C   Anti Fast Cycle Flow Temperature Hysteresis, (settable)  2C to 15C, default 6C

 

His is set, 12 minutes and 7C.

The "anti fast cycle time" is actually the last  running time of the burner, if the last running time was 12 minutes or more then the boiler will refire when the flow temperature falls to target temp - 7C, if the boiler then runs for say only 5 minutes before the next burner cut then it will not look at the flow temperature for (12-5), 7 minutes, if the flow temperature has then fallen to target temp - 7C (or more) then the burner will refire. This would seem to indicate that the minimum anti cycle time is the time taken for the flow temperature to fall to the target flow temp - 7C.

 

       

Edited Thursday at 13:34 by John Carroll

[JohnMo]

But this mechanism is to protect the boiler, nothing more nothing less.  Short cycling is just a quick way to empty your bank balance. You heat the boiler, pipework and a load of energy goes out the flue and maybe you still have a cold house.

 

If you boiler is in that mode, you maybe have way to many zone, badly set up heating system, or another issue, or all the above.

[marshian]

On 18/12/2025 at 13:33, John Carroll said:

Vaillant use a table of time+target temp.

 

It took me a long time to get my head round the Vaillant/Glow Worm table for anti cycling

 

 

It's heavily linked to the flow temps used - basically at higher temps you really don't get much anti cycle time at all regardless of what you set the parameter to.

[John Carroll]

I think they are exactly the same as the Vaillant ones.

The Set maximum burner anticycle time determines the actual anticycle time.

The default setting of 20C means the maximum anticycle time is 20 minutes in the very unlikely event that the target/flow temp is 20C, if (for the same 20C setting) the target/flowtemp is 60C then the anticycle time is only 6 minutes which makes sense because the return&flow temperatures will fall quite alot with the circ pump continuing to run so gives the boiler better leeway to get away on refiring and prevent the burner to trip again at targettemp+5C, if you find 6 minutes is still insufficient then you can change the anticycle time to say 30C which gives a anticycle time of 9 minutes at a target/flow temp of 60C which might then allow the boiler to get away in one refiring, and so on, clever enough if using outside temperature compensation or the like. Vaillant were/are? notorious for maintaing ignition conditions for 60 seconds or so after refiring before allowing modulation from ~ 65% firing, most boilers will allow modulation after 10 secs or less after flame detection or whatever.

Do Vaillant own Glowworm??

 

Vaillant anticycle times

 

Edited 3 hours ago by John Carroll

[SimonD]

49 minutes ago, John Carroll said:

Do Vaillant own Glowworm??

 

Yes, they're part of the same group.

[marshian]

19 minutes ago, SimonD said:

 

Yes, they're part of the same group.

Yeah just making a cheaper product range with less functionality 

 

with a 24kW condensing fas boiler with a 10kW min that hit the circuit with 65% of max on every restart I had to utilise the anticycle table to manage the boiler fires to a sensible number of cycles per hour - it had a 39 deg min flow temp but it was hopeless trying to run that low 45 deg was just about possible in shoulder seasons but once in winter proper it was 50 or above which meant it short cycled a fair bit